MMWD narrows Sonoma-to-Marin pipeline options

Board members expressed concern over cost estimates, which ranged between $140 million and $380 million.

Aiming to boost the county’s water supply, the Marin Municipal Water District is exploring the idea of connecting pipelines in Petaluma and Cotati to its reservoirs.

District staff presented three main potential projects — narrowed from 13 — at Tuesday’s board of directors meeting.

“It’s getting exciting every time we whittle that list down,” board member Matt Samson said.

The pipelines would transport water from the Russian River into Marin reservoirs. Treated Russian River water is transported to Marin through a 9-mile aqueduct along the Highway 101 corridor from Petaluma to North Marin Water District in Novato. The district then sends the water directly to the Marin Municipal Water District’s water distribution system.

Board members expressed concern over cost estimates, which ranged between $140 million and $380 million.

In February 2023, the board selected a roadmap for improving water supply. The aim of the project is to enhance the reliability, flexibility and resiliency of the district’s water system to improve service to customers.

Tim Taylor of Carollo Engineers, an environmental engineering firm hired by the district, recommended three alternatives. All three projects would be phased in design and construction.

The first would involve connecting the pipelines to NMWD’s aqueduct system. Phase one would include a pipeline from Stafford Lake to the MMWD’s Soulajule Reservoir. Phase two would add another pipeline connecting Stafford Lake to the existing NMWD aqueduct system. An additional phase would add a pipeline to Nicasio Reservoir, part of the MMWD system.

The project would total 16.2 miles and could increase supply by 24 million gallons per day. Its capital cost is estimated at $129 million to $196 million.

A second option presented would use the same aqueduct system and add a pipeline via San Antonio Road to the Soulajule Reservoir. Later phases would build a pipeline system from water tanks in Cotati down to Kastania and connect the new Soulajule pipeline to Nicasio Reservoir.

This alternative would add 14.8 miles of pipeline and cost between $148 million and $378 million. It could increase supply by up to 39 million gallons per day.

The last option, and most expensive with an estimated cost of $380 million, would involve new construction along the Highway 101 corridor through downtown Petaluma and to the Soulajule Reservoir. The next phase would extend it to the Nicasio Reservoir. It could increase water supply by 30 million gallons per day.

Options involving Stafford Lake and the south transmission system — a network of pipes and pump stations in southern Sonoma County — were ruled out as standalone projects because they did not significantly increase the water supply.

The list was narrowed to three by evaluating criteria like how it would increase resiliency, its overall sustainability, the environmental and community impacts and the project’s flexibility and feasibility.

“So what would represent a favorable criteria score would be a project that adds some substantial sustainable dry-year yield,” said Paul Sellier, the district’s water resources director. “If it was a project that allowed us to adapt to climate change, for example.”

Board member Larry Russell said the budget estimates were concerning, and wondered if the district would need that much water.

“These are big dollars,” Russell said. “I’m concerned that we’re at levels that are too high for the district to afford any of the alternatives.”

Board member Jed Smith said the cost estimates raise questions about how financial feasibility was weighed in the options.

“It does kind of make you question the scoring,” Smith said. “That should have knocked it out to zero.”

District staff said more information, including specific costs and environmental constraints, needs to be gathered.

Ben Horenstein, district general manager, said a more detailed analysis of costs and funding was yet to come, but said he recognized that it is a significant issue.

“I think it’s important for the public to understand that if we want the perfect system, it’s going to be really expensive,” Samson said. “So we have to understand what is going to be the best for our money.”

A final recommendation is expected to be made to the board this summer.